A continental perspective on the timing of environmental change during the last glacial stage in Australia

Abstract

The timing and duration of the coldest period in the last glacial stage, often referred to as the last glacial maximum (LGM), has been observed to vary spatially and temporally. In Australia, this period is characterised by colder, and in some places more arid, climates than today. We applied Monte-Carlo change point analysis to all available continuous proxy records covering this period, primarily pollen records, from across Australia (n = 37) to assess this change. We find a significant change point occurred (within uncertainty) at 28.6 ± 2.8 ka in 25 records. We interpret this change as a shift to cooler climates, associated with a widespread decline in biological productivity. An additional change point occurred at 17.7 ± 2.2 ka in 24 records. We interpret this change as a shift towards warmer climates, associated with increased biological productivity. We broadly characterise the period between 28.6 (± 2.8) – 17.7 (± 2.2) ka as an extended period of maximum cooling, with low productivity vegetation that may have occurred as a combined response to reduced temperatures, lower moisture availability and atmospheric CO2. These results have implications for how the spatial and temporal coherence of climate change, in this case during the LGM, can be best interrogated and interpreted.

Environmental change during the last glacial on an ancient land bridge of southeast Australia

“…However, the aforementioned mid‐latitude pollen records indicate an earlier shift in vegetation and extended LGM period from ~30–28 to 18–17 ka, which is consistent with our pollen record for the Bass Strait area (Figure 4). While the timing of the LGM remains debatable (Hughes et al, 2013), our result lend support to existing views on an extended LGM timing in the Southern Hemisphere, including in lower latitudes (Cadd et al, 2021; Petherick et al, 2017).…”

“…The nature of the environmental shift and timing is consistent with vegetation change recorded for other mid–high latitude areas in both hemispheres (including Northern Hemisphere land bridges), as well as global climatic and sea‐level shifts during the last glacial period (e.g. Ager & Phillips, 2018; Cadd et al, 2021; Lambeck et al, 2014; Langgut et al, 2011; Newnham et al, 2007; Figure 4).…”

“…Our palaeoecological data reveal a major environmental change in the region around 29 ka, which featured a shift from a wet wooded landscape during MIS 3 to a dry grassy landscape during MIS 2 and into early MIS 1 (Figure4). The nature of the environmental shift and timing is consistent with vegetation change recorded for other mid-high latitude areas in both hemispheres (including Northern Hemisphere land bridges), as well as global climatic and sea-level shifts during the last glacial period (e.g Ager & Phillips, 2018;Cadd et al, 2021;Lambeck et al, 2014;Langgut et al, 2011;Newnham et al, 2007;. Figure 4).4.1.1 | Early glacial environmental changes on the Bassian Land BridgeThe pollen composition and percentage abundance in Crystal Lagoon during the interval ~35-29 ka are comparable to pollen assemblages in the basal zone of records from Hunter Island and King Island(D'Costa et al, 1993;Hope, 1978; Figure4), as well as a recently published record of a single early-glacial sample from Flinders Island(Ladd & Clarke, 2020).…”

The Application of Pollen Radiocarbon Dating and Bayesian Age-Depth Modeling for Developing Robust Geochronological Frameworks of Wetland Archives

“…The two sedimentary sequences used in this study are both located on the eastern seaboard of Australia (Figure 1). Previous studies examining sedimentary sequences extracted from these locations suggest that both records extend beyond the last glacial maximum (Black et al 2006;Cadd et al 2018;Lewis et al 2020;Forbes et al 2021), a rare occurrence in Australia (Cadd et al 2021). However, previous work from sedimentary records in these locations has identified major outliers in the 14 C chronologies (Lewis et al 2020;Forbes et al 2021), indicating the need for a more targeted approach to the development of 14 C chronologies for these important records.…”

“…Age uncertainties are important when comparing multiple palaeoenvironmental records and assessing the synchronicity of events across records and identifying drivers of change. There still remain few examples of studies that integrate the inherent age uncertainty from age-depth models when conducting metaanalyses (Anchukaitis and Tierney 2013;Cadd et al 2021;Tierney et al 2013;Tyler et al 2015). The most common approach remains the application of "best-fit" or mean modeled age for individual depths, with little consideration paid to age uncertainties or precision.…”